1. Field of the Invention
The present invention relates to an electrical connector having a shield frame to shut off an electrical noise, and more particularly to an electrical connector to be used as a socket (hereinafter referred to as socket).
As a socket so arranged as to shut off an electrical noise, there is known a socket in which the peripheries of contact pieces held by the socket body are surrounded by a metallic casing shield frame having projections. An electrical connector to be used as a plug (hereinafter referred to as plug) is selected as the counter member of the socket of the type above-mentioned. The plug has also a shield frame surrounding the peripheries of contact pieces. When the plug is inserted into the socket, the shield frame of the plug locally comes in contact with the projections of the shield frame of the socket. In such a contact state, the shield frame of the socket may be electrically securely connected to the shield frame of the plug. Thus, the shield frames may produce an excellent shielding effect as compared with the arrangement where the shield frames come in surface contact with each other.
2. Description of Related Art
Generally, the resiliency of a metallic plate used for the shield frame of a socket is not so great. Accordingly, a conventional socket is made such that, as shown in FIG. 12, a metallic plate is bent in the form of a casing to form a shield frame F and the ends of the metallic plate abut each other at an abutting portion Fl. The abutting portion Fl is located in the longitudinally center portion of the bottom wall of the shield frame F and projections T are formed in the vicinity of the abutting portion Fl.
When the socket is formed in the manner as shown in FIG. 12, the distance l between the abutting portion Fl and one end of the bottom wall of the shield frame F is relatively long. Accordingly, even though the resiliency of the metallic plate is not so great, the projections T are apt to be resiliently vertically displaced with the ends of the bottom wall serving as fulcrum points. In this connection, even though the socket S or a plug to be inserted in or removed from the socket S is twisted at the time of the insertion or removal of the plug, this does not involve the likelihood that the contact pressures between the projections T and the shield frame of the plug are damaged so prematurely.
However, when the plug is inserted in and removed from the conventional socket S, the shield frame of the plug gets over the projections T or is separated therefrom so that the bottom wall of the shield frame F is vertically displaced. Accordingly, when the socket S is to be mounted on a printed circuit board, it is required to form, between the bottom wall of the shield frame F and the printed circuit board, a space for allowing the bottom wall to be displaced. This presents the problem that the height of the socket S as mounted on the printed circuit board is increased by such an amount as to provide the space above-mentioned.
Further, in order that the projections T are satisfactorily maintained as contacted with the plug shield frame and the plug is smoothly inserted/removed in/from the socket S, it is required to enhance the precision at which the casing shield frame F of the socket S is fitted to the plug shield frame. This results in increased cost. Further, the increased fitting precision may assure good contacts between the projections T and the plug shield frame and smooth insertion/removal of the plug. On the other hand, however, there remarkably appears the influence of twist of the socket or plug when the plug is inserted in or removed from the socket. This disadvantageously causes the bottom wall of the shield frame F to be readily deformed.